1. Field of the Invention
This invention relates to a shunt connected superconducting energy stabilizing system with isolation switching for providing energy to an AC or DC load or loads and/or to a source of electrical power. In particular, the invention relates to a superconducting stabilizing system providing energy to the loads, during voltage sags or momentary losses of power, while an isolation switch disconnects the loads from the source of power. In addition, the superconducting energy stabilizing system can supply energy to both the loads and to the source at the same time until the source of electrical power recovers from the energy sag or momentary loss of power.
2. Background of the Prior Art
Prior art superconducting energy storage systems have been directed to the storage of energy derived from an alternating current (AC) power system and to the return of the stored energy to the AC power system. Typically energy is stored during periods of low energy demand when surplus energy exists and is returned to the power system when energy demand is high.
One such system appears in Peterson et al., U.S. Pat. No. 4,122,512. Peterson et al. uses a reversible alternating to direct current converter to convert the alternating current obtained from the AC power system into direct current for storage in a superconducting magnet and for converting the stored direct current into alternating current for return to the AC power system. This type of system, while providing for the efficient storage and return of energy to the AC power system, is not directed to supplying energy directly to loads.
Another superconducting energy storage system described in Higashino, U.S. Pat. No. 4,695,932, discloses an energy storage circuit which converts three-phase alternating current to direct current for storage in a superconducting energy storage coil. A DC capacitor and chopper circuit are used to control the amount of direct current in the superconducting energy storage coil. According to Higashino, this configuration allows the current capacity of the AC supply line equipment and the converter to be scaled down in accordance with service power established by the current rating of the coil, and also allows a reduction of operation losses.
These known superconducting energy storage systems provide for the efficient storage and return of energy to an electrical power system, but do not provide a means for disconnecting the power system from the loads which receive the power and supplying stored energy directly to the loads only. Such systems must therefore generate enough energy to support the entire power system and any loads connected thereto. This high level of support necessarily means that these superconducting energy storage systems must be fairly large not only in current and energy capacity but also in physical size.
Visser et al., U.S. Pat. No. 4,962,354, issued to Superconductivity, Inc. on Oct. 9, 1990, describes a superconductive voltage stabilizer. The superconductive voltage stabilizer comprises an AC/DC converter, a voltage regulator, an energy storage cell and a superconducting energy storage coil. Alternating current is converted to direct current and is stored in a superconducting energy storage coil. The stored direct current is released to an energy storage cell which in turn delivers the energy to a load. Energy is released in a controlled fashion according to the energy requirements of the load to thereby maintain the load's operation. This patent, U.S. Pat. No. 4,962,354, is incorporated herein by reference.